Recovery of potassium chloride



July 9, 1963 B. P. EDMONDS ETAL 3,096,969

RECOVERY OF pomssmu CHLORIDE Filed May 26, 1961 tmoflma U02 5 243 zoEjom Ur v-UOM bum E23 662 -26 UV.

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@L Q J JAMES a. mums M BYE. P/(AZRS warm/s70 ATTO/P/VEY United States Patent 3,096,969 RECOVERY OF POTASSIUM CHLORIDE Byron P. Edmonds, Alice, and James B. Dahms and Edward Phelps Helvenstou, Corpus Christi, Tex., assignors to Pittsburgh Plate Glass Company, Pittsburgh,

Pa., a corporation of Pennsylvania Filed May 26, 1961, Ser. No. 123,916 7 Claims. (Cl. 262-3) This invention relates to a novel method of mining potassium chloride deposits. Potassium chloride usually occurs in mineral deposits closely associated with sodium chloride. In many cases, the potassium chloride exists in admixture or in combination with sodium chloride in the form of a potassium chloride-rich stratum (containing 15 to 60 percent by weight of KCl based upon the total weight of KCl and NaCl in the stratum) or a plurality of such seams which are disposed immediately above other strata which are lean as to potassium chloride, i.e., contain less than 15 percent KCl by weight based upon the weight of NaCl and KCl therein, or which contain no substantial amount of potassium chloride but which are preponderantly sodium chloride. These minerals, of course, frequently contain other materials, such as calcium sulfate, magnesium sulfate and the like.

Deposits of potassium chloride and sodium chloride of this type frequently are very deep. For example, deposits of this character which are located in Canada often are 5,000 feet or more below the surface of the ground.

Although some KCl has been produced from natural brines or from sodium chloride brines, as a practical matter substantially all of the potassium chloride recovered from underground is obtained by shaft, room and pillar type of mining in which the potassium chloridecontaining mineral is removed in solid state from the deposit and carried to the surface where it is treated by specially designed techniques to separate potassium chloride.

A number of proposals have been made for the recovery of potassium chloride by extraction with Water. So far as can be ascertained, none of these processes have achieved commercial success. Serious difficulty is encountered in establishing a proper cavity because of the slow rate of extraction of KCl from the deposit, and also because crystals of both potassium chloride and sodium chloride tend to form in the cavity or the well through which the liquor is circulated, thus plugging up the system and rendering it essentially inoperative.

According to the present invention, these difliculties have been solved in a simple manner. In the practice of the process herein contemplated, a well is drilled through the potassium chloride-rich stratum or deposit and downwardly into the zone in which the potassium chloride concentration is low, i.e., below 15 percent based upon the weight of KCl and NaCl, or is substantially non-existent and where the sodium chloride is comparatively high. At this point, water or an aqueous solution which is unsaturated as to sodium chloride is caused to flow down the well either through a pipe disposed in the well or through the concentric area within the well but outside the pipe, and the potassium chloride-lean, sodium chloride-rich strata is extracted to establish a cavity in the manner well known to the art of extracting sodium chloride from subterranean deposits thereof.

In order to cause the cavity to grow laterally, a water immiscible inert fluid, which may be air, nitrogen or like inert gas, but preferably a liquid which has a density lower than that of water at the temperature of operation, such as mineral oil, crude or refined petroleum oil or like liquid hydrocarbon, is fed into the cavity in order to establish a thin layer at the roof thereof. This causes the cavity to expand laterally as water is fed into the well and the sodium chloride dissolved and aqueous sodium chloride solution withdrawn from the well.

After the cavity in the sodium chloride-rich, potassium chloride-lean deposit has been increased to a substantial size, for example, when the cavity has a minimum diameter of about 15 feet, preferabiy at least 25 feet (as computed by measurement of the weight or volume of sodium chloride or like salt which has been removed from the deposit and established logging tet hniques for determining the depth of the cavity), the level of the roof is gradually allowed to rise. This is accomplished by raising the point of water injection into the cavity and, if necessary, either discontinuing the introduction of oil or like fluid into the well with the incoming Water or cutting down the flow rate of such fluid to a very substantial degree. As a consequence, further extraction continues by virtue of the water flow into the well and aqueous solution withdrawn therefrom until the protective layer becomes so thin that it ceases to prevent extraction of salt from the roof of the cavity. Gradually, then, the roof of the cavity is allowed to rise until it reaches the potassium chloride strata. After the cavity has penetrated the potassium chloride-rich strata to a convenient depth, for example, several inches or more, the oil or other like fluid, which has a density less than that of water, is fed into the cavity along with water and the extraction of the potassium chloride-rich strata is then commenced. Of course, this is immediately detected by an increase in the concentration of potassium chloride in the brine escaping from the well.

The brine thus obtained then rises in potassium chloride content and an operating equilibrium is reached. A brine containing about 4 to 60 pounds of potassium chloride and 30 to 35 pounds of sodium chloride per pounds of water is obtained. The exact composition of the brine will vary considerably, depending upon the temperature of the strata. Extraction of potassium chloride from the deposit can be continued by feeding water down the well either as such or as a solution which is unsaturated both as to potassium chloride and sodium chloride, and extracting the resulting aqueous solution. The average level of the roof of the cavity normally is above the level of water introduction.

The level of the roof is gradually raised at a controlled rate through the KCl-rich deposit 'by control of the level of water introduction into the cavity and the amount of mineral oil or like hydrocarbon liquid fed therein.

By following the above process, the difficulties previously encountered in potassium chloride extraction are substantially eliminated. Thus, there is established a relatively large cavity in the sodium chloride strata so that when the roof of the cavity is raised into the potassium chloride strata there is adequate room in the cavity for any intrinsic crystallization which can take place, since the crystals which form and any impurities which may be insoluble can settle to the bottom of the cavity without disturbing or hindering contact of the incoming water with the KCI deposit.

Moreover, the cavity is large enough to accommodate a body of brine so large that any cooling of the brine solution which tends to take place as a consequence of the extraction of potassium chloride is minimized by the already large body of brine in the cavity. Thus, localized cooling and consequent crystallization and plugging of equipment is minimized. Furthermore, the face of the KCl-rich cavity undergoing extraction is then large enough so that, despite the fact that potassium chloride dissolves at a relatively slow rate, recovery of potassium chloride by the extraction process can be effected at a practical and a commercial rate.

It will be understood that the rate of solution of potassium chloride is comparatively slow. For example, it is frequently found that this rate is in the range of 0.2 to 0.8 pound per hour per square foot extracting surface at a practical operating temperature, for example, 45 C. This means that extraction of enough potassium chloride to develop a well to the point where practical recovery of potassium chloride can be effected is an extremely slow and difficult problem. In small cavities it can become so slow that after a short time, any extraction which takes place in the potassium chloride-rich strata substantially ceases because of the tendency of the surface of the strata to accumulate a crystalline deposit rich in NaCl which hinders passage of water to the KCl. On the other hand, by establishing a large cavity in the sodium chloride-rich strata, such a large surface can be established that, despite the slow rate of potassium chloride recovery, 21 brine having a practical concentration of potassium chloride can be recovered.

Reference is made to FIGURE 1 which is a diagrammatic illustration of mining potassium chloride deposits in accordance with this invention.

Referring to FIGURE 2, there is illustrated a second and preferred method of mining potassium chloride in accordance with the instant invention.

This process is diagrammatically illustrated in FIG. 1 of the drawing. As shown in FIG. 1, a well suitably fitted with a casing 1 is drilled through the bed rock into the subterranean deposit, through the potassium chloride-rich layer and into the potassium chloride-lean, sodium chloride-rich layer. The potassium chloride-rich layer may have the following approximate composition:

Percent by weight KC] I- 16 to 40 Water insoluble clay About 1 to 5. Calcium sulfate 1 to 2. Water soluble calcium and magnesium Water soluble calcium and magnesium salts, such as MgCl MgSO and Ca[HCO About 2.

NaCl Remainder.

The potassium chloride-lean or sodium chloride-rich deposit may have the following typical composition:

Percent by weight KCl O to 15.

NaCl Remainder.

There is then disposed a. pipe 2 concentrically within the casing l of the well. Water is then caused to flow down the well in order to extract the sodium chloride rich deposit. In the embodiment. as illustrated, the water is allowed to flow downwardly in the space between the pipe and the casing and substantially saturated sodium chloride is withdrawn from the lower part of the cavity as it is formed. An immiscible fluid which has a density lower than of water and which is insoluble in or immiscible with water (preferably hydrocarbon oil) is fed in small amounts (usually in amounts up to about pounds of such agent per cubic foot of salts withdrawn) into the well along with the water. As a consequence, this fluid forms a protective layer 6 at the upper portion of the cavity 8 which is produced.

The amount of such fluid which is introduced should be enough to establish a layer of /2 to 2 inches at the top of the cavity in order to protect the roof thereof. This amount can be computed roughly by estimating the ap proximate volume or" the cavity from the number of tons of sodium chloride which is extracted from the well. Usually about 0.] to 10 pounds of hydrocarbon oil is fed per cubic foot of salts withdrawn.

In general, it is not necessary to drill into the sodium chloride-rich layer to any great depth. Usually extraction of NaCl from the NaCl-rich deposit is conducted at a level 1 to 15 feet below the level of the potassium chloride-rich deposit which it is ultimately desired to extract.

As a consequence of the operation, water is caused to flow rapidly into the well and a solution of sodium chloride withdrawn therefrom, and the cavity enlarges laterally to one of substantial size, for example, preferably 25 feet or more in diameter.

After the cavity has been so enlarged, the level is raised, as described above, by decreasing inflow of oil to the well and continuing introduction of water and withdrawal of brine. The level of water introduction usually is raised at the same time so that water flows outwardly from. the cavity approximately at the upper portion of the pool of brine. This may be done by cutting holes in the well casing or by raising the casing. Finally, the level of the roof of the cavity is allowed to rise to the point where extraction of substantial potassium chloride from the KCl-rich strata is allowed to commence. Thereafter, the KCl extraction is conducted while controlling the level of the cavity roof so that it rises at a very gradual rate through the KCl-rich deposit as described above.

According to a preferred embodiment of the invention, it is desired to effect extraction of potassium chloride through a pair of wells. Thus, it is more desirable to conduct the extraction by feeding water or a partially unsaturated aqueous solution down one well and withdrawing the resulting KCl-sodium chloride brine from the brine pool from another well. This is accomplished as diagrammatically illustrated in FIG. 2. As shown therein, two wells 11 and 21 are drilled and developed substantially, as has been described above, by establishing cavities in the sodium chloride-rich deposit. Extraction of the sodium chloride solution from the sodium chloride-rich deposit is continued from one or from both of the wells until the cavity 8 has been caused to expand laterally to the point where it is in communication with both wells. The level of the cavity is then allowed to rise through the potassium chloride-lean, sodium chloride-rich deposit until it reaches the potassium chloriderich deposit. There is then established the cavity 8 as diagrammatically shown in FIG. 2. This cavity has a thin layer of the inert, immiscible fluid 6 comparable in character to the layer discussed in connection with FIG. 1.

When the wells are in communication and have been raised to a point where the roof of the cavity is above the bottom of the KCl-rich deposit, water is fed down well 11 and potassium chloride-sodium chloride solution is withdrawn from well 21, usually from a level below that at which water is introduced through well 11 and often at or near the bottom of the cavity but above the level where crystals or insoluble impurities have accumulated to an appreciable degree. Alternatively, a solution of sodium chloride and potassium chloride, which is unsaturated as to both sodium chloride and potassium chloride, may be fed down the well. In any event, whether water or a sodium chloride-potassium chloride solution is fed down well 20, care generally is taken to extract both sodium chloride and potassium chloride substantially in the proportions that they exist in the deposit. This can be effected conveniently simply by balancing the sodium chloride content of the solution going into well 11.

As has been previously mentioned, potassium chloride absorbs heat when it is dissolved in water. To compensate for this, it is desirable that the temperature of the Water or sodium chloride-potassium chloride solution fed down the well 11 be at least 10 to 20 F. higher than the temperature of the potassium chloride brine coming from well 21. By this means, heated solution is supplied to the pool of brine in the cavity 8 and thus undue cooling of this cavity is prevented. Also, the layer 6 of inert immiscible fluid is established and maintained by feeding up to about 10 pounds of mineral oil or like liquid hydrocarbon per cubic foot of salt removed.

Such normally liquid hydrocarbons are most desirable for establishing protective layer 6 for a number of reasons. In the first place, these liquids more effectively resist extraction of the roof and, therefore, prevent an excessive rate of roof extraction. Furthermore, the control of the top level of the cavity can be more easily accomplished with a liquid than with air or like gas.

The above process can be continued until the level of the cavity has been raised to the top of the potassium chloride seam and until the cavity has been expanded as far as practicable. Frequently, it is possible to continue the extension of the cavity laterally until the amount of salt extracted therefrom indicates extraction of a cavity having a radius of 200 to 500 or more feet measured from the well. Of course, it is very difiicult to measure exactly a cavity of this character. However, it is possible to estimate the size of the cavity in terms of the amount of sodium chloride and potassium chloride removed therefrom and the known composition and den sity of the deposit.

For most purposes, it is desirable to extract both sodium chloride and potassium chloride from a deposit substantially in the proportions in which these two materials exist in the deposit. This is desirable in order to avoid the possibility that the rate of aqueous dissolution of the deposit decreases to an impractical degree. However, after the deposit has become very large, for example, after the width or lateral extension of the cavity has reached 350 feet, as computed from the volume of sodium chloride and potassium chloride and like salts removed from the deposit, it is then possible in many cases to reduce the amount of sodium chloride being extracted. By this time, the cavity is large enough so that extraction of potassium chloride from the sodium chloride deposit can be effected at a practical rate by feeding brine which is saturated as to NaCl but unsaturated as to KCl into the cavity. Often, even in such instances, to 50 percent of the sodium chloride existing in the deposit can be extracted from the deposit with the potassium chloride, leaving the remaining 50 to 95 percent of the sodium chloride in the deposit. This, of course, can be accomplished by feeding to the cavity a brine which con tains sodium chloride but is unsaturated as to NaCl and KCl and in which the KCl to NaCl ratio is lower than that of the deposit.

It will be understood that the process herein contemplated is subject to numerous variations. For example, the cavity used to commence dissolution of the potassium chloride may be formed by means other than extraction. Thus, a cavity may be excavated or formed by fracturing in the lower sodium chloride-rich layer or stratum or in the louver portion of the potassium chloride-rich stratum and then the roof of the cavity gradually raised through the potassium chloride-rich stratum by extraction as described above.

More than two wells may be installed in communication with a single cavity and operated as contemplated herein.

Although the present invention has been described with reference to specific details of certain embodiments thereof, it is not intended that such details should be regarded as limitations upon the scope of the invention except insofar as included in the accompanying claims.

What is claimed:

1. A method of recovering potassium chloride from a deposit having a potassium ch1oride-rich stratum and containing sodium chloride disposed above a sodium chloride deposit in which the potassium chloride content is relatively lower than in the potassium chloride-rich deposit which comprises drilling a well into the sodium chloride-rich deposit, extracting sodium chloride with water from the sodium chloride-rich deposit until a cavity of substantial size has been produced and then continuing such extraction and raising the roof of the cavity until the roof reaches the potassium chloride-rich deposit and thereafter extracting potassium chloride with water from the potassium chloride-rich strata.

2. A method of recovering potassium chloride from a deposit having a potassium chloride-rich stratum and containing sodium chloride disposed above a sodium chloride deposit in which the potassium chloride content is relatively lower than in the potassium chloride-rich deposit which comprises establishing a cavity at least 25 feet in dinameter adjacent the lower part of said potassium chloride-rich stratum with an upper face in contact with said stratum, feeding water into said cavity and thereby dissolving potassium chloride to form a brine, withdrawing the brine and gradually raising the level of said roof as extraction proceeds.

3. A method of recovering potassium chloride from a natural deposit which contains sodium chloride and at least 15 percent potassium chloride by weight thereof which comprises establishing a cavity having a diameter of at least 25 feet adjacent the lower part of said deposit, feeding water into said cavity thereby dissolving potassium chloride to form a brine, withdrawing brine, and gradually raising the level of the cavity roof as extraction proceeds.

4. The process of claim 3 wherein extraction is continued until the diameter of the cavity is at least 350 feet and thereafter potassium chloride is selectivel extracted from sodium chloride in the deposit.

5. A method of recovering an aqueous brine containing potassium chloride and sodium chloride from a deposit having a potassium chloride-rich stratum and containing sodium chloride disposed above a sodium chloride deposit in which the potassium chloride content is relatively lower than in the potassium chloride-rich deposit which comprises drilling a well into the sodium chloride-rich deposit, extracting with water the sodium chloriderich deposit until a cavity of substantial size has been produced and then continuing such extraction and raising the roof of the cavity until the roof reaches the potassium chloriderich deposit is extracted with water which is an unsatuand potassium chioride with water from the potassium chloride-rich strata in substantially the proportions the sodium chloride and potassium chloride exist in the pot assium chloride-rich strata.

6. The method of claim 5 wherein the sodium chloriderich deposit is extracted with water which is an unsaturated sodium chloride solution.

7. The method of claim 5 wherein the potassium chloride-rich deposit is extracted with water which is sodium chloride-potassium chloride solution unsaturated with respect to both said salts.

References Cited in the file of this patent UNITED STATES PATENTS 1,960,932 Tracy May 29, 1934 2,331,890 Cross Oct. 19, 1943 2,822,158 Brinton Feb. 4, 1958 

1. A METHOD OF RECOVERING POTASSIUM CHLORIDE FROM A DEPOSIT HAVING A POTASSIUM CHLORIDE-RICH STRATUM AND CONTAINING A SODIUM CHLORIDE DISPOSED ABOVE A SODIUM CCHLORIDE DEPOSIT IN WHICH THE POTASSIUM CHLORIDE CONTENT IS RELATIVELY LOWER THAN IN THE POTASSIUM CHLORIDE-RICH DEPOSIT WHICH COMPRISES DRILLING A WELL INTO THE SODIUM CHLORIDE-RICH DEPOSIT, EXTRACTING SODIUM CHLORIDE WITH WATER FROM THE SODIUM CHLORIDE-RICH DEPOSIT UNTIL A CAVITY OF SUBSTANTIAL SIZE HAS BEEN PRODUCED AND THEN CONTINUING SUCH EXTRACTION AND RAISING THE ROOF OF THE CAVITY UNTIL THE ROOF REACHES THE POTASSIUM CHLORIDE-RICH DEPOSIT AND THEREAFTER EXTRACTING POTASSIUM CHLORIDE WITH WATER FROM THE POTASSIUM CHLORIDE-RICH STRATA. 